Fantasy novel about women (lovers) with psychic abilities in pairs, but they split up

I read this book in the 1990's. It was high fantasy. There were women who had e.s.p. I don't remember if they had clairvoyance or dream interpretation or mind reading abilities or what specifically, but they worked best in pairs. The main character was pair-bonded to another woman, but for some reason, they split up, and she goes on a journey to another land, I think. That's all I remember. 
I think you're thinking of Tarma and Kethry? But they weren't lovers - it was more of a blood-sister thing - and the other bits about the psychic abilities seems wrong for them. I don't think they spent significant time apart after taking on their oath, either.

Worth a shot for the OP to look at, still - the books about them were The Oathbound and Oathbreakers.
Tarma and Kethry?
No, I looked at the author's site, and I don't think that's what I am looking for. Thanks, though!
Re: Mercedes Lackey?
Ah well. I haven't read those books in ages, but from what I remembered they seemed similar to what you were looking for.

Good luck with your hunt!
Could it have been one of the Hadra series by Diana Rivers? The first one, Journey to Zelindar, was published in 1987, and two more appeared in the 90's. There have been others since.

Author's website
Publisher
Hadra series?
Maybe? It's hard to tell from the brief synopsis on the author's site. I'll have to look for these books.
Not Darkover Either
Someone else suggested it might be from the Darkover Series by Marion Zimmer Bradley, but I don't think so, because those books have a outer space element I don't remember, plus if I had read and enjoyed one of those books, I would've read more in the series, and I've never read them.
There's a pretty good chance that this is Kristine Kathryn Rusch's "Heart Readers". The detail about two women whose magic only works when they're "together" is fairly distinctive, and it's a major plot point of "Heart Readers".